Unconventional Crystals

Seminar series
Physical Chemistry Seminar
Mon, Oct 7 4:00pm
2033 Young Hall
Speaker Professor Vinothan N. Manoharan
Harvard University
Dept. of Physics


Abstract: Crystal growth is a venerable field, but there are still phenomena to be discovered.  I will discuss two sets of experiments on colloidal crystals – crystals made from micrometer-scale spherical particles -- that grow in unconventional ways.  The first set of experiments examines attractive colloidal particles on the surfaces of spherical water droplets. These particles form crystalline domains that are long, slender, and ribbon-like, as opposed to the more isotropic domains that grow in bulk.  Interestingly, they contain no topological defects.  I will show how the elastic stress arising from the Gaussian curvature of the droplet causes the crystals to grow in this way.  Our results, which show that curvature can fundamentally alter the growth of ordered domains, may have implications for self-assembly on other curved manifolds, such as vesicles or viral capsids.

The second set of experiments examines crystallization of particles with grafted DNA strands.  Using a DNA reaction known as strand displacement, we design a system in which crystals grow when the melt is heated – the opposite of the usual behavior. In fact it is possible to "program" all sorts of unusual phase transitions simply by changing the thermodynamics of the strand displacement reactions.  This programmability could enable new self-assembly schemes similar to those employed by biological systems.